Investigations on the field of geopolymeric binders, state that this new material is likely to
have high potential to become an alternative to Ordinary Portland cement (OPC). Recent
results on the Life Cycle Analysis (LCA) of geopolymers they have a lower impact on global warming than OPC but on the other side they have a higher environmental impact regarding other impact categories. Lower CO2 emissions geopolymers are therefore needed. Classical two part geopolymers could be made more eco-efficient with a lower carbon dioxide footprint if the use of sodium silicate is avoided. Besides current geopolymeric mixes can suffer from efflorescence originated by the fact that alkaline and/or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation. Therefore new and improved geopolymer mixes are needed. One-part geopolymers (sodium silicate free) were described by the first time in 2008 still a lot of issues remain unexplained about them. This paper compares the durability performance of one-part geopolymers with OPC mortars. The obtained results revealed that replacing 70% Portland cement by 58.3% Fly ash, 4% calcined stuff and 7.7% calcium hydroxide results in satisfactory and promising results in durability tests

Abdollahnejad, Zahra

Aguiar, J. L. Barroso de

Jesus, Carlos M. G.

Pacheco-Torgal, F.

Universidade do Minho: RepositoriUM

WASTES: Solutíons, Treatments and Opportunities2nd Intemational ConferenceSeptember 11th - 13th 2013ONE-PART GEOPOL YMERS VERSUS ORDINARY PORTLAND CEMENT (OPC)Mortars: DURABILlTY ASSESSMENTZ. Abdollahnejad", C. JeSUS2, F. Pacheco-Torqar' and J. B. Aquiar"1 Department of Civil Engineering, University of Minho, Guimaraes, Portugal.tolumahvash@gmail.com2 Departmentof Civil Engineering,Universityof Minho,Guimaraes, Portugal. cjesus@civil.uminho.pt3 C-TAC Research Centre, Department of Civil Engineering, University of Minho, Guimaraes,Portugal. torgal@civil.uminho.pt4 C-TAC Research Centre, Department of Civil Engineering, University of Minho, Guimaraes,Portugal.aguiar@civil.uminho.ptABSTRACTInvestigations on the field of geopolymeric binders, state that this new material is likely tohave high potential to become an alternative to Ordinary Portland cement (OPC). Recentresults on the Life Cycle Analysis (LCA) of geopolymers they have a lower impact on globalwarming than OPC but on the other side they have a higher environmental impact regardingother impact categories. Lower CO2 emissions geopolymers are therefore needed. Classicaltwo part geopolymers could be made more eco-efficient with a lower carbon dioxidefootprint if the use of sodium silicate is avoided. Besides current geopolymeric mixes cansuffer from efflorescence originated by the fact that alkaline and/or soluble silicates that areadded during processing cannot be totally consumed during geopolymerisation. Thereforenew and improved geopolymer mixes are needed. One-part geopolymers (sodium silicatefree) were described by the first time in 2008 still a lot of issues remain unexplained aboutthem. This paper compares the durability performance of one-part geopolymers with OPCmortars. The obtained results revealed that replacing 70% Portland cement by 58.3% Flyash, 4% calcined stuff and 7.7% calcium hydroxide results in satisfactory and promisingresults in durability tests.Keywords: Geopolymers; ordinary Portland cement; fly ash; durability performance.INTRODUCTIONWith an annual production of almost 3 Gt Ordinary Portland cement (OPC) is the dominant binder ofthe construction industry [1]. The production of one tonne of OPC generates 0.55 tonnes of chemicalCO2 and requires an additional 0.39 tonnes of CO2 in fuel emissions for baking and grinding,accounting for a total of 0.94 tonnes of CO2. Other authors [2] reported that the cement industryemiUed in 2000, on average, 0.87 kg of CO2 for every kg of cement produced. As a result the cementindustry contributes about 7% of the total worldwide CO2 emissions [3]. The projections for the globaldemand of Portland cement show that in the next 40 years it will have a twofold increase reaching 6Gt/year. The urge to reduce carbon dioxide emissions and the fact that OPC structures which havebeen build a few decades ago are still facing disintegration problems points out the handicaps ofOPC. Portland cement based concrete presents a higher permeability that allows water and otheraggressive media to enter leading to carbonation and corrosion problems. The early deterioration ofreinforced concrete structures based on ordinary Portland cement (OPC) is a current phenomenonwith significant consequences both in terms of the cost for the rehabilitation of these structures, oreven in terms of environmental impacts associated with these operations. Research works [4-8]carried out so far in the development of geopolymers showed that much has already beeninvestigated and also that an environmental friendly alternative to Portland cement is rising.Besides the durability of geopolymers is still a subject of some controversy [9]. While Duxon et aI. [10]state this is the most important issue on determining the success of these new materiais and otherauthors [11] mention that the fact that samples from the former Soviet Union that have been exposedto service conditions for in excess of 30 years showing liUle degradation means that geopolymers dotherefore appear to stand the test of time. Sut since those materiais were of the (Si+Ca) type thatconclusion cannot be extended to geopolymers defined as "alkali aluminosilicate gel, with aluminium115and silicon linked in a tetrahedral gel framework" [12]. On the other side Juenger et aI. [1] argue that"The key unsolved question in the development and application of alkali activation technology is theissue of durability" and more recently Van Deventer et aI. [13] recognized that "whether geopolymerconcretes are durable remains the major obstacle to recognition in standards for structural concrete".Efflorescences is an important drawback of two part geopolymers that so far has received very littleattention. This phenomenon is influenced by several causes like the reactivity of the alumino-silicate,the mix composition and the curing conditions. According to Skvara et aI. [14,15] the bond betweenthe sodium ions (Na+) and the aluminosilicate structure is weak and that explains the leachingbehaviour. Kani et aI. [16] showed that efflorescences can be reduced either by the addition ofalumina-rich admixtures or by hydrothermal curing at temperatures of 65 °e or higher. These authorsfound that the use of 8% of calcium aluminate cement greatly reduces the mobility of alkalis leadingto minimum efflorescences (this cement has 28% of CaO). These results are very important becausethey constitute a step back in the development of geopolymers. For one the use of hydrothermalcuring nas serious limitations for on-site concrete placement operations. On the other hand the use ofcalcium based mixtures reduces the acid resistance and raises the chances for the occurrence ofASR. This means that this subject merits further investigations. One-part geopolymers represent akey event on geopolymer technology having been described by the first time in 2008. In this work,obtained experimental results from durability tests on a novel kind of mixes termed one-partgeopolymers are presented.EXPERIMENTAL WORKMATERIALSThe composition of dry mix in this study was: ordinary Portland cement (OPC), fly ash, kaolin, sodiumhydroxide, calcium hydroxide, water and superplasticizer (SP). A mixture of kaolin and sodiumhydroxide which is calcined in a furnace at 650 °e during 140 minutes. The cooled mixture is calledcalcined stuff. The OPC used was type 42,5 R with a clinker content between 95-100% and with aspecific weight of 3.15 g/cm3 and a Blaine fineness of 3842 cm2/g. The SP was used to maintain auniform consistency between the different mixes. The chemical composition of the fly ash complieswith the minimum requirements indicated in EN-450-1 [16] for being used as a partial replacement ofcement in concrete. Based on this standard the fly ash was categorized in class B and group N forthe loss of ignition and fineness, respectively and it has a specific weight of 2.42 g/cm3.Table 1. Mixture proportions (%)Name OPC Flyash Ca(OH)z Calcined Water 5P 5andstuffOPC100 100 ---- ---- ----- 35 0.8 80OPC70- FL30 70 30 ---- ----- 35 0.8 80OPC30-FL58.3-CH7.7-C54 30 58.3 7.7 4 35 0.8 80OPC26-FL58.3-CH7.7-C58 26 58.3 7.7 8 35 0.8 80OPC18-FL58.3-CH7.7-C516 18 58.3 7.7 16 35 0.8 80EXPERIMENTAL TESTSFour experimental tests were carried out to evaluate the material behavior. The first stage wasassigned to evaluate the material under compression while other stages were assigned to durabilitytests. In the second, third and fourth stages were conducted capillarity, immersion and acid attacktests, respectively. Hence, experimental producer of water absorption by immersion, water absorptionby capillarity and resistance to acid attack are explained in the following:Water absorption by immersionSpecimens were tested with 28 days curing. The specimens were immersed in water at roomtemperature for 24 hours. First the weight of the specimens while suspended by a thin wire andcompletely submerged in water is recorded as Wim (immersed weight). After that the specimens wereremoved from water, and placed for 1 min on a wire mesh allowing water to drain, then visible surfacewater is removed with a damp cloth and weight is recorded as Wsat (saturated weight). Ali specimensare placed in a ventilated oven at 105°C for not less than 24 hours and allowing that two successiveweightings at intervals of 2 hours show an increment of loss not greater than 0,1% of the lastpreviously determined weight of the specimen. The weight of the dried specimens is recorded asWdry (oven-dry weight). Absorption coefficient is determined as following equation:A(%)= wsat -wdry X 100 (1)w.s-«:116Water absorption by capillarityThe test was done according to BS EN 1015-18:2002. For performing the capillary test, threespecimens were cast and tested with dimension 100x100x100 rnrn''. The preparation of testspecimen was done as follows: after drying in an oven at 105°e for 60 hours, they are water proofalong their lateral surface with a fine layer of silicon in order to reduce water evaporation andguaranty capillarity water absorption.Resistance to acid attackThe cubic specimens with dimension 50x50)(50 rnrn" were used to evaluate this criterion for acidattack. The weights of specimens were measured and then saturated in a salutian which cantains of10% H2S04 acid (In volume). The weights of specimens were measured for 7, 14, 28 and 56 daysand the appearance of specimens were also observed.RESUL TS ANO OISCUSSIONSCOMPRESSIVE STRENGTHFigure 1 shows the compressive strength results. The reduction of OPC content leads to a highreduction on the compressive strength of the mortars. The slow hydration characteristics of fly ashcontribute to explain that reduction. The mixture with just 30% OPC (and 58.3 fly ash, 7.7 calciumhydroxide and 4% calcined stuff) shows an almost 40% reduction in compressive strength whencompare to the reference mixture. Since this mixture has a higher percentage redudion on OPCcontent this could mean that the addition of metakaolin and calcined sodium hydroxide could havecompensated that reduction. However, the use of increase content in calcined stuff does not seem tocompensate the ope reduction. Thus meaning that the use of 4% calcined stuff seems to be anoptimum content.90 l~ 80 l-; 70 ~ -tQ 60c!!:! 50 J"li: I41 40 1.~ 30 ~41;.. 20~ 10u o -f--L---'====="-OPC100014[J28...-.---OPC 70-FL 30 OPC30-FL58.3-CH OPC26-Fl58.3-CH OPC18-H 58.3-CH7.7-(54 7.7-(58 7.7-(516Figure 1. Compressive strengthWATER ABSORPTION BY IMMERSIONThe results of water absorption by immersion are presented in Figure 2. Since ali the mixtures havethe same w/b ratio they should present a similar open porosity. So the differences between theseveral mixtures could be explained by the scatler data because they are small enough for that. Ofcourse the different hydration products present in the different mixtures may contribute for theporosity differences but only in a very slight manner. Thats why the mixture already mention in theprevious section as havin a ood com ressive stren th erformance shows the lower o en orosity.20~c'~15:e412106'+:e-5o'"..cct oOPC100 OPC70-Fl30 OPC30-H 58.3-CH OPC26-Fl 58.3-CH OPC18-Fl58.3-CH7.7-(54 7.7-(58 7.7·(516Figure 2. Absorption coefficients for different specimens117WATER ABSORPTION BY CAPILLARITYFigure 3 shows the results of the capillary water absorption and the water absorption capillaritycoefficients are showed in Figure 4. The reference mixture shows the best performance of them alI.On the opposite side the mixture with 26% OPC 58.3 fly ash, 7.7 calcium hydroxide and 8% calcinedstuff clearly shows a very high water absorption by capillarity even at early ages. Such performance istypical of a microstruture with a high amount of capillary pores. The three remaining mixtures show asimilar ca illa water absor tion coefficient indicatin a similar internal ca illa ore network.1,60E-01 _OPC26-FL5. - . -CS8-- .. -- OPC1001,40E-01 - -OPC70-FL30• • • • • •• OPC 30-FL SB 3-CH 7 7 -CS 4S 1,20E-01 - - OPC18-FL583-CHú-csã_ 1,OOE-01'-('>I2 E 8,OOE-02 I~ .[ 6,OOE-02 ~- ......•....••.• ; (.••• VI •••• to •• •••~ -400E-02 ".~ ....• .:.:.: _ - - - ~r<~ 2:00E-02. ~~:;:::;::~--- ... - ----------------------- ..§.~O,OOE+OO ~" , , , i " I"" I ' , , , I ' , , , i ' , , , I " -'--1--'--'--'-----1O 7.000 8.000S 3,: I~ 3~~ 2,5';: E1~1'~LoD,~ 1u:= 0,5<1/8 o ~--~ L ~ __ ~ ~~~~ ~ __ ~ _osc 100 ore 70 - Fl30 osc 30-FL58.3-Q-I esc 26-Fl58.3-Q-I osc 18-FL58.3-Q-I7.7-CS4 7.7-CS8 7.7-CS16Figure 4. Water absorption capillarity coefficients-RESIST ANCE TO ACID ATTACKThe results of mass loss for specimens exposed to 10% sulphuric acid solutions are shown in Figures5..1day 03 day 07 day260 ~240220- 200 l~ 180 ~i 160 1"" 140'ij 120~ 100 l;S 80 ~ r-l~ ~~L_dJ.L-..w-- ruOPC100dJOPC70-FL30 OPC30-FL 58.3-CH OPC26-FL 58.3-CH OPC 18-FL 58.3-CH7.7-CS 4 7.7-C58 7.7-C516Figure 5. Weight loss after sulphuric acid atlackAfter 1 day the best results are shown by the reference mixture and also by the mixture in which 30%OPC was replaced by fly ash. Since the reference mixture has much lower capillary water absorption118than the other mixes this means that in a short term the rate of acid ingress contributes to explain theobserved results. However, this is not the case of the one part geopolymeric mixture with 8% calcinedstuff because since it has the highest capillarity coefficient it should have a higher weigth loss thanthe other geopolymeric mixtures. Afier 3 days exposure to acid attack one can confirm that the weigthloss is proportional to the OPC content in the mixtures. A higher OPC content is associated to a lowerweight loss. High pozzolan content mixtures showed lower resistance to acid attack this results do notconfirm previous findings about the fact that the presence of pozzolanic admixtures was found tolower the detrimental effect of acid atlack on concrete [17,18]. Probably because a densermicrostructure typical of pozzolanic based mixtures were not yet formed by the time this mixtureswere tested.CONCLUSIONSIn this study, the durability of OPC mortars and the durability of one part geopolymer mortars wereassessed using three different tests (water absorption by immersion, water absorption by capillarityand resistance to acid attack). Compressive strength results were also presented showing that thereduction of OPC content in the mortars leads to a high reduction on the compressive strength. Theaddition of fly ash is not enough to compensate the OPC reduction due to its slow hydrationcharacteristics. In the geopolymeric mixtures the one with of 4% calcined stuff seems to correspondto a good compromise between a low OPC content and an acceptable compressive strength. Theresults of water absorption by immersion are very similar for ali the mixtures which is due to the factthat they have the same w/b ratio. The capillary water absorption is very high for the one partgeopolymeric mixtures with 8% calcined stuff indicating a microstructure with very high amount ofcapillary pores. The results of resistance to acid attack show that the weight loss is proportional to theOPC content in the mixtures.ReferencesM. Juenger, F. Winnefeld, J. Provis and J. Ideker, (2011), Advances in alternative cementitiousbinders, Cement and Concrete Research Vol. 41, pp.1232-1243.J. Damtofi, J.Lukasik, D. Herfort, D. Sorrentino and E. Gartner, (2008), Sustainable developmentand climate change initiatives, Cement and Concrete Research Vo1.38, pp.115-127.M.Taylor and D. Gielen, (2006), Energy efficiency and C02 emissions from the global cementindustry, International Energy Agency.F. Pacheco-Torgal, J. Castro-Gomes and S. Jalali, (2008), Alkali - activated binders: a review Part1 Historical background, terminology, reaction mechanisms and hydration products,Construction and Building Materiais Vo1.22, pp.1305-1314.F. Pacheco-Torgal, J. Castro-Gomes and S. Jalali, (2008), Alkali - activated binders: a review Part2 About materiais and binders manufacture, Construction and Building Materiais Vo1.22,pp.1315-1322.C. Li, H. Sun and L. Li, (2010), A review: The comparison between alkali-activated slag (Si+Ca) andmetakaolin (Si+AI) cements, Cement and Concrete Research Vo1.40, pp.1341-1349.F. Pacheco-Torgal, Z. Abdollahnejad, S. Miraldo, S. Baklouti and Y.Ding, (2012), An overview onthe potential of geopolymers for concrete infrastructure rehabilitation, Construction andBuilding Materiais Vo1.36, pp.1053-1058 .F. Pacheco-Torgal, Y. Ding, S. Miraldo, Z. Abdollahnejad and J. Labrincha, (2012), Aregeopolymers more suitable than Portland cement to produce high volume recycledaggregates HPC ?, Construction and Building Materiais Vo1.32, pp.1048-1 052.F.Pacheco-Torgal, Z. Abdollahnejad, A. Camões, M. Jamshidi and Y.Ding, (2012), Durability ofalkali-activated binders. A clear advantage over Portland cement or an unproven issue ?",Construction and Building Materiais Vo1.30, pp.400-405.P. Duxson, J.Provis, G. Luckey and JVan Deventer, (2007), The role of inorganic polymertechnology in the development of "Green Concrete". Cem Concr Res Vo1.37, pp.1590-1597.J. Van Deventer, J.Provis and P. Duxson, (2012), Technical and commercial progress in theadoption of geopolymer cement, Minerais Engineering Vol. 29, pp.89-104.P. Duxson and J. Van Deventer, (2009), Geopolymers, Structure, Processing, Properties andApplications, Ed. J. Provis & J. Van Deventer, Woodhead Publishing Limited Abington Hall,Cambridge, UK.F. Skvara, L. Kopecky, V. Smilauer, L. Alberovska and Z. Bittner, (2008), Material and structuralcharacterization of alkali activated low-calcium brown coal fly ash, Journal of HazardousMateriais Vo1.168, pp.711-720.F. Skvara, L. Kopecky, V. Smilauer, L. Alberovska and L. Vinsova, (2009), Aluminosilicate polymers119- Influence of elevated temperatures, efflorescence, Ceramics - Silikaty Vo1.53, pp.276-282.E. Kani, A. Allahverdi and J. Provis, (2011), Efflorescence control in geopolymE~rbinders based onnatural pozzolan, Cement and Concrete Composites Vo1.34, pp.25-33.NP EN 450-1, Fly ash for concrete - Part 1: Definition, specifications and conformity criteria.[17] R. Beddoe, K. Schmidt, (2009), Acid aUack on concrete - effect of concrete composition. Part1.Cem Int;7:88-94.[18] S. Goyal, M. Kumar, D. Sidhu, B Bhattacharjee, (2009), Resistance of mineral admixtureconcrete to acid attack. J Adv Concr Technol 7:273-83.120

One-part geopolymers versus Ordinary Portland Cement (OPC) mortars : durability assessment

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Universidade do Minho: RepositoriUM